Multi-functional exterior structural foam sheathing panel

ABSTRACT

An insulating sheathing panel has an insulating core, such as foam, sandwiched between PMDI impregnated cover sheets. The resulting panels offer structural reinforcement as well as insulating qualities to a building framework.

This is a continuation of application Ser. No. 07/680,810, filed Mar.22, 1991, now issued U.S. Pat. No. 5,220,760.

BACKGROUND OF THE INVENTION

This invention relates to exterior sheathing panels useful in buildingconstruction.

To provide adequate resistance to lateral forces, such as seismic andwind forces, all buildings typically must have bracing attached to theframework of the exterior walls. The materials and labor required toinstall such bracing adds to the expense of construction. Bracing isgenerally provided by the application of one or a combination of thefollowing materials to the exterior building walls: metal, wood,plywood, or other reconstituted wood based panels located at the cornersand spaced apart at certain distances along the walls. Alternatively,panels made from wood, laminated paperboard or gypsum wallboard areplaced about the entire perimeter of the building for reinforcingpurposes.

Insulating panels are also commonly placed on the exterior framework ofa building. Such panels, which are used to retard heat transfer throughthe exterior walls, are commonly made of polystyrene, polyurethane, orphenolic foams or glass fiber materials. Sheets of metal foil, used toprevent foam aging, are adhered to the planar surfaces of panels madefrom such materials. Insulating panels known to the inventor do not havesufficient shear strength and fracture toughness to significantly bracethe framework of a building. Therefore, additional exterior wall bracingis used with these insulating panels.

An additional problem associated with available insulative sheathingproducts is the propensity for such products to puncture or break duringeither transportation or construction. In light-frame housingconstruction, workers frequently attach the sheathing to the studsbefore placing the wall in an upright position. Workers often walk ontop of the panels in order to attach the panels to the studs. Walking onknown insulating panels can cause them to rupture.

A recurring problem associated with available sheathing is thetemperature related expansion and contraction of the panels which causesthe panels to retract from the supporting nails. Once a panel retracts,a pathway is created for the infiltration of air and moisture, whichreduces the overall thermal performance of the panels.

Therefore, a need exists for improved insulating sheathing panelsdirected toward overcoming these and additional problems of the priorart.

SUMMARY OF THE INVENTION

The invention is directed to a structural insulating sheathing systemconsisting of a laminated panel configuration that exhibits excellenttensile strength and fracture toughness. The sheathing panel is designedto meet governmental wind and seismic bracing criteria for residentialconstruction purposes. The strength and composition of the panel allowsit to function as a bracing system as well as an insulating system, andthereby simplifies the construction process. In addition, the strengthof the panel reduces the degree of care workers must exercise inhandling the panels.

As a first aspect of the invention, a panel is preferably comprised ofan insulating core sandwiched between tough fibrous sheets. The core istypically composed of a plastic foam material, such as polyisocyanuratefoam, but may be composed of a variety of other materials including, butnot limited to, polystyrene, polyurethane, or phenolic foams. Thesematerials are light-weight and rigid. First and second cover sheets aresecured to the opposed major surfaces of the core. These cover sheets,or sheet facers, are composed of tough polyisocyanate impregnatedcellulosic fibers which have been cured by heat and pressure. In thesecover sheets, the naturally occurring binders of the cellulosic fiberhave been removed and replaced by a polyisocyanate resin.

The sheets are produced using polyisocyanate resin, which may be dilutedwith an organic solvent and thereafter applied to the fibers. The fibersare generally arranged in a sheet and the resin is applied to both sidesof the sheet, such as by spraying, dipping or any other convenientmethod. After the resin is cured by applying heat and pressure, thecover sheets may be adhered to the core, as by adhesive. Alternatively,the cover sheets may be adhered to the core by the foam which forms thecore as the foam is cured between the cover sheets.

Fibrous cover sheets of different thicknesses can be used on oppositesides of the core for particular construction purposes. For example, athicker sheet may be used on the surface of the core to be spaced fromthe building framework where the greatest impact or other abuse islikely to occur. When mounted to the framework of the building, theinsulating sheathing material of the present invention comprised of thefoam core and tough cover sheets exhibits excellent tensile strength andshear modulus. Therefore, the panel can function as a unitary bracingsystem on the building framework.

Typical foam cores have blowing agents, such as freon, trapped withinthe closed cells of the core during formation. Sheets of foil may beprovided between the core and the cover sheets to block the exchange ofthe blowing agent and air. The loss of blowing agent over time thatwould otherwise occur would interfere with the thermal insulationproperties of the core. Foil may also be placed at the exterior of thecover sheets as well.

Additionally, one or more layers of weather-protective material may beprovided on the exterior surface of one or both of the cover sheets. Theweather-protective material, when used, is best applied as a sheet or asa coating. Layers on opposite sides of the panel can be of the same ordifferent thickness and may be made of the same or different materials.Examples of such weather-protective materials, in addition to metallicfoils, may include polyethylene films, water sealant coatings andpaints. The use of weather-protective materials protects the cover sheetand may also enhance the insulating properties of the panel.

A second aspect of the invention relates to a fastening system forattaching the panels to building frames, such as the stud frames used inresidential construction. The fastening system includes both mechanicaland chemical fasteners which can be used in combination or separately toattach the panels to the frame.

The preferred mechanical fasteners are generally galvanized large-headroofing nails or staples. These fasteners, whether used separately or incombination, provide a sufficient shear strength to support both thepanel and to withstand the forces to which the panel is subjected. Thepreferred chemical fastener is generally an exterior constructionadhesive. Once the adhesive cures, it provides a strong chemical bondbetween the panel and the building framing.

Additional features, objects and advantages of this invention will beevident from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded, partial cross-sectional view of a panel accordingto the present invention and also showing adjacent studs of the frame ofan exterior building wall;

FIG. 2 is an exploded, partial cross-sectional view, taken along line2--2 of FIG. 1; and

FIG. 3 is an oblique view showing the panels of the invention installedon the frame of an exterior building wall.

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2, a sheathing panel 10 comprises fibrous sheets12, optional vapor-impervious sheets 16, and an insulating core 20. Thevapor-impervious sheets 16 may be metallic foil or another selectedlaminate. The core 20 preferably comprises a lightweight rigidinsulating plastic material such as a plastic foam. Fibrous sheets 12are laminated to the vapor-impervious sheets 16, such as by an adhesive14. The fibrous sheets 12 are secured directly to the core 20 in theevent the vapor-impervious sheets 16 are not used. If used, thevapor-impervious sheets 16 are adhered to the core 20 by an adhesive 18.The adhesive 14, 18 is typically an exterior flame-resistant and lowsmoke producing material, such as a urethane-based adhesive. Onespecific example is MOR-AD from Morton Thiokol Company.

The core 20 is typically composed of a ply of rigid polyisocyanurateplastic foam, such as a closed-cell polyisocyanurate foam. A preferredembodiment of the core 20 has a core thickness of one-half inch;however, the thickness of the core 20 can be varied over a wide range,such as from about one-eighth to about four inches. Polyisocyanuratefoam, when used as the core 20, has a foam density from about one toabout four lbs/ft³. A specifically preferred polyisocyanurate foam has adensity of about two lbs/ft³, a thickness of one-half inch, and athermal conductivity of 0.134 Btu in/ft² hr °F. The shear strength ofsuch a polyisocyanurate core ranges from about fifteen to abouttwenty-five psi. The shear modulus of such a core ranges from about 500to about 1,000 psi. Of course, other core materials may also be used,including plastic foams having other formulations.

A fibrous cover sheet 12 may be attached directly to each major planarsurface of the core 20, or to exposed major planar surfaces of sheets 16(if used), thus sandwiching the core 20 therebetween. Each of the coversheets 12 comprises at least one ply of a fibrous material impregnatedwith polyisocyanate. The polyisocyanate loading is preferably from about8% to about 20% w/w of polyisocyanate to the fibrous material.

Preferably the fibrous material is a cellulosic fibrous material, suchas substantially delignified cellulose fibers. Such fibers can beobtained from chemical pulp, thermomechanical pulp, recycled fiber, andthe like. The fibers can be in the form of non-woven bleached orunbleached paper or paper-like materials, woven mats, sheets or felts,and the like. Delignified cellulosic fibers are obtained by conventionalprocesses wherein naturally-occurring lignins are substantially removed.The purpose of delignification is to remove lignin and other resinouscomponents from the cellulose molecules comprising the fibers so as toexpose and make available a greater number of hydroxyl groups on thecellulose molecules for bonding reactions with isocyantes.

The cellulosic material is preferably arranged in a sheet form which hasan ability to absorb liquids. A preferred cellulosic material is "kraftliner board," as is known in the art. A preferred basis weight of linerboard is within a range of from about 42 to about 69 lb/ft². Kraft linerboard having a basis weight of 58 lb/ft² is particularly suitable.

The cellulosic material should include a small amount of moisture.Generally, the maximum limit of moisture in the fibers is about 10% w/wwater relative to the weight of the cellulose, where the water moleculesare generally present as water of dehydration in association with thehydrophilic cellulose fibers. Additional moisture can be added, ifrequired, to the cellulose fibers, such as by applying steam to thefibers, a procedure which may result in improved impregnation of thecellulosic fibers with the polyisocyanate resin.

A preferred resin for the cellulosic fibers is poly(diphenylmethanediisocyanate), referred to in the art as PMDI. Other organicpolyisocyanates are usable as long as they possess at least twoisocyanate (--NCO) groups per molecule. At least two isocyanate groupsare required in order to form cross-linked polymeric materials.

For use in impregnating the cellulosic fibers, the polyisocyanate resinis generally diluted with an organic solvent, such as propylenecarbonate, in an amount up to about 20% w/w organic solvent relative tothe polyisocyanate. Diluting the polyisocyanate in this manner conferssurprisingly improved mechanical properties to the resultingpolyurea-cellulose composite, when compared to similar composites madeusing "neat" (undiluted) polyisocyanate. Approximately 20% w/w solventto isocyanate is regarded as a practical upper limit, since increasingthe solvent above this level also results in additional absorption ofwater.

The liquid resin comprising a solution of polyisocyanate inorganicsolvent can be applied to the cellulosic material in any manner whichensures satisfactory impregnation of the cellulosic fibers. Satisfactoryimprenation of the cellulosic fibers with the resin occurs with aloading range of about 8% to about 20% w/w resin relative to the weightof the cellulose. Since the cellulosic material is typically in sheetform, the resin can be applied to one or preferably both sides of thecellulosic sheet by spraying, dipping, rolling, or other means. Thecellulosic material may be impregnated with polyisocyanates either by abatch process or by a continuous process.

Following impregnation of the cellulosic material with the resin, theimpregnated sheet is cured by the simultaneous application of heat andpressure for a time which typically does not exceed about five minutes.The temperature required to cure the resin is typically within a rangeof from about 105° C. to about 245° C. and the pressure is typicallywithin a range of from about 130 psi to about 1,200 psi.

An additional example of a method of forming the fibrous sheets 12 canbe found in U.S. patent application Ser. No. 07/618,723, filed Nov. 27,1990, and entitled "Isocyanate Modified Cellulose Products and Methodfor Their Manufacture," which application is incorporated herein byreference.

Sheets 12 of the polyisocyanate impregnated and cured cellulosicmaterial are applied to at least one and preferably both of the majorsurfaces of a rigid substrate, such as the plastic or foam core 20.Single or multiple sheets of the material can be applied to either oneor both of the planar surfaces of the core 20.

The preferred thickness of the fibrous cover sheets attached to core 20is about 0.023 inches (e.g. two plys of 58 lb. kraft liner material),although the thickness may vary such as from about 8.5×10⁻³ to 0.1inches. The preferred density of cover sheet 12 is about 65-70 pcf,which exhibits a tensile strength of from about 18,000 to about 24,000psi in the machine direction (in the major plane of the cover sheets)and a stiffness (Young's modulus) of from about 1.8×10⁶ to about 2.2×10⁶psi in the machine direction.

When a panel is formed of cover sheets of this construction (forexample, two-plies of 58 lb. kraft liner board, loaded with from about8% w/w to about 20% w/w PMDI and cured to from 65-70 pcf), it has beenfound to have a machine direction linear expansion at from 50% to 90%humidity and 65° F. of less than 0.1 inch per inch in the majordirection. Therefore, a panel of excellent stability is provided. Also,such a panel has a water vapor transmission rate of at least 3.5 permswhen tested in accordance with ASTM D2646. Moreover, such a panel hasbeen found to have a water absorption at 96 hours of no more than about6.5% when tested according to ASTM D2642. Furthermore, tests of such apanel pursuant to ASTM C318 confirmed that the panels had a thermalconductivity (with a one-half inch core) of no more than about 0.134 Btuin/h·ft² ·°F. In addition, the modulus of rupture of such a panel in themajor plane was at least about 800 psi in the major plane (machinedirection) and about 200 psi in the cross machine direction, when testedper ASTM C393.

Laminated between the polyisocyanate impregnated cellulosic fiber 12 andthe core 20, if used, are blowing agent retaining sheets such asmetallic foil sheets 16 which generally have a thickness of from about2.5×10⁻³ to about 9.0×10⁻³ inches. The foil may be adhered to thefibrous material 12 by a one-component urethane solids adhesive 14, aspreviously described.

The sheathing panels can be produced in a continuous process or a batchprocess. In a typical continuous process, the treated and cured fibrouscover sheets are continuously unrolled and supported with a gaptherebetween. The foam forming material is injected into this gap andfills the gap with foam, the foam attaching itself to the cover sheets.Individual panels are then cut from the sheets (e.g. four feet wide byeight or nine feet long panels). In a batch process, treated and curedfibrous cover sheets are typically adhesively secured to preformed foampanels. In either case, foil 16 may be and preferably is, interposedbetween the foam core and cover sheets.

If used, the metallic foil is generally primed with adhesive on bothsides for better adhesion to the insulating core and fibrous sheet 12,using adhesives as previously described. Metallic foil 16 can be adheredto either or both sides of the core 20.

Various weather protection materials may also be incorporated into thesheathing panel. Examples of such materials include layers ofpolyethylene film, urethane resin, paint, water sealant coatings oraluminum foil. If used, preferably one or more layers of such a materialare applied to the outwardly-facing or exposed planar surface of one orboth of the fibrous sheets 12. Also, siding 50 may be placed over theexposed outer surface of the panels 10.

The panels can be used in a number of ways to insulate and bracelight-frame houses and other buildings. For instance, when panels 10 aremounted at the corners of a conventional building stud frame as shown inFIG. 3, no additional bracing is required at the corners. The panels canbe secured to the frame either by mechanical or adhesive fasteners,separately or in combination. For additional bracing, the panels of theinventor can be positioned at the corners and also at intervals alongthe perimeter of the wall, or around the entire perimeter of thebuilding.

To attach the panels to stud frames using adhesive, adhesive istypically applied either to the exterior surface of the studs or to theportions of the panel which are to contact the studs. For example, a 1/4to 3/8 inch bead of adhesive may be applied uniformly to all framingcomponents. Alternatively, a thin veneer of adhesive may be applied tothe region of the panel ultimately contacting the studs. Exemplaryadhesives include construction adhesives such as Morad, 100%solids/solvent adhesive from Morton Thiokol Company and H. B. Fuller Maxbond. Once the adhesive is applied, the sheathing panel 10 maythereafter be secured to the studs by using, for example, broad-headgalvanized iron roofing nails 30, having a 3/8 inch head diameter.Alternatively, 7/16 inch crown galvanized wire staples can be used tosecure the panel to the studs. The nails or staples can be applied usinga pneumatic gun set to 40 to 50 psi air pressure, and are most effectivewhen evenly spaced at 3 inches center-to-center spacing at the perimeterand at 6 inches center-to-center spacing on all other intermediatesupports. The broad-head galvanized nails or galvanized staples can beused to provide adequate pressure while the adhesive is curing; however,the mechanical fasteners or chemical fasteners can be used singularly.Other mechanical fasteners may of course also be used.

When panels having treated cover sheets and a one-half inch thick foamcore were mounted to a standard "two" by "four" lumber framework (2×4studs, standard and better grade, on 16 inch center-to-center spacingwith a single bottom or sole plate and a double top plate, the rackingshear strength determined under ASTM E-72 Test Standard was (1) at least9,000 lbs. when the panels were mounted with a combination of a 3/8 inchbead of H. B. Fuller Max bond construction adhesive and either No. 11gauge, 11/2 inch long large head galvanized roofing nails (3"center-to-center spacing at the edge of the panels and 5"center-to-center spacing in the field of the panels intermediate to thepanel edges or 7/16" crown, 16 guage, 11/2" legs galvanized staples atthe same spacing as the nails, and following curing or drying of theadhesive; (2) 3,500 lbs. for these nails at this spacing without theadhesive; and (3 ) 2,600 lbs. for these staples at this spacing withoutthe adhesive. The primary function of the nails and staples whenadhesive is used is to hold the panels in place until the adhesive sets.These mechanical fasteners can be eliminated if quick setting adhesiveor other means for holding the panels in place is used. Also, theracking shear strength without the mechanical fasteners and with onlythe adhesive would also be expected to be at least 9,000 lbs. followingthe curing of the adhesive, however, some other mechanism (such asclamps or gravity) would be used to hold the panels in place, ifnecessary) while the adhesive cures.

Having illustrated and described the principles of my invention withreference to several preferred embodiments, it should be apparent tothose of ordinary skill in the art that the invention may be modified inarrangement and detail without departing from such principles. I claimas my invention all such modifications which fall within the scope ofthe following claims.

I claim:
 1. A sheathing panel comprising:a core sheet of a manufacturedcellular material having first and second major opposed surfaces; firstand second cover sheets secured to the respective first and second majoropposed surfaces with the core sheet therebetween, the first and secondcover sheets each comprising at least one sheet of cellulosic materialimpregnated with polyisocyanate within a range of about 8% to 20% byweight of polyisocyanate to cellulosic material with the polyisocyanatebeing heat cured.
 2. A panel according to claim 1 in which each of themajor opposed surfaces of the core sheet is overlayed with a respectiveblowing agent retaining sheet.
 3. A panel according to claim 2 in whichthe blowing agent retaining sheets are comprised of a metallic foil. 4.A panel according to claim 1 in which at least one of the cover sheetsis overlayed with a thermal reflective material.
 5. A panel according toclaim 4 in which the thermal reflective material comprises a metallicfoil.
 6. A panel according to claim 3 in which at least one of the coversheets is overlayed with a thermal reflective material.
 7. A panelaccording to claim 1 in which the cover sheets are cellulosic paper orpulp sheets.
 8. A panel according to claim 1 in which the core has ashear strength of from at least about 10 to about 30 psi and a shearmodulus of from at least about 500 psi to about 1,000 psi, the coversheets having a machine direction tensile strength of from about 1.8×10⁴to 2.4×10⁴ psi in the major plane of the cover sheets and a Young'smodulus in the machine direction of from about 1.8×10⁶ psi to about2.2×10⁶ psi.
 9. A panel according to claim 8 in which the core has athickness of from about 1/8 to 4 inches and a density in the range offrom about 1 to about 4 pounds per cubic foot.
 10. A panel according toclaim 9 in which the cover sheets have a thickness of from about8.5×10⁻³ inch to about 0.1 inch.
 11. A panel according to claim 10including a thermal reflective material overlaying at least one of thecover sheets.
 12. A panel according to claim 10 including a respectiveblowing agent retaining sheet between the core sheet and each of thecover sheets.
 13. A panel according to claim 1 in which the cover sheetscomprise cellulosic liner material impregnated with from about 8% to 15%by weight of polyisocyanate to cellulosic material, which is cured to adensity of from about sixty-five to about seventy pcf, and having amachine direction linear expansion at from 50% to 90% humidity and 65°F. of less than 0.1 inch per inch in the major direction.
 14. A panelaccording to claim 1 in which the cover sheets comprise cellulosic linermaterial impregnated with from about 8% to 15% by weight ofpolyisocyanate to cellulosic material, which is cured to a density offrom about sixty-five to about seventy pcf, and having a water vaportransmission rate of at least 3.5 perms.
 15. A panel according to claim1 in which the cover sheets comprise cellulosic liner materialimpregnated with from about 8% to 15% by weight of polyisocyanate tocellulosic material, which is cured to a density of from aboutsixty-five to about seventy pcf, and having a water absorption at 96hours of no more than about 6.5%.
 16. A panel according to claim 1having a thermal conductivity of no more than about 0.134B.T.U.:in/h.f².°F.
 17. A panel according to claim 1 having a modulus ofrupture in the major plane of at least about 800 psi.
 18. A panelaccording to claim 1 in which the first and second cover sheets are ofdiffering thicknesses.
 19. Plural panels according to claim 1 mounted atleast to a corner of a conventional building stud frame without otherreinforcing bracing at such corner, the panels being secured to theframe by an adhesive and having a racking shear strength of at least9,000 lbs.
 20. Plural panels according to claim 1 mounted at least to acorner of a conventional building stud frame without other reinforcingbracing at such corner, the panels being secured to the frame bymechanical fasteners only and having a racking shear strength of atleast 2,600 lbs.
 21. A conventional building stud frame having cornerswith plural sheathing panels mounted at least to a corner of thebuilding stud frame without other reinforcing bracing at such corner,the panels each comprising a core sheet of a manufactured cellular foammaterial having first and second major opposed surfaces, the core sheethaving a thickness of from about 1/8 to 4 inches and a density in therange of from about one to about four pounds per cubic foot, first andsecond cover sheets at least one of which includes polyisocyanate in therange of about 8 percent to 20 percent by weight of polyisocyanate tocellulosic material, the first and second cover sheets being secured tothe respective first and second major opposed surfaces with the coresheet therebetween.
 22. A conventional building stud frame with mountedplural sheathing panels according to claim 21 with a racking shearstrength of at least 2,600 lbs.
 23. A conventional building stud framewith mounted plural sheathing panels according to claim 21 with aracking shear strength of at least 3,500 lbs.
 24. A conventionalbuilding stud frame with mounted plural sheathing panels according toclaim 21 with a racking shear strength of at least 9,000 lbs.
 25. Aconventional building stud frame with mounted plural sheathing panelsaccording to claim 21 and in which the sheathing panels each have a coresheet with the major opposed surfaces overlaid with a respective blowingagent retaining sheet.
 26. A conventional building stud frame withmounted plural sheathing panels according to claim 25 and in which thesheathing panels each have at least one cover sheet overlaid with athermal reflective material.
 27. A conventional building stud frame withmounted plural sheathing panels according to claim 21 and in which thesheathing panels each have at least one cover sheet overlaid with athermal reflective material.
 28. A sheathing panel comprising:a coresheet of a manufactured cellular foam material having first and secondmajor opposed surfaces, a thickness of from 1/8 to four inches and adensity in the range of from about one to about four pounds per cubicfoot; first and second cover sheets secured to the respective first andsecond major opposed surfaces with the core sheet therebetween, thefirst and second cover sheets each comprising at least one sheet ofcellulosic material with polyisocyanate within a range of about 8percent to 20 percent by weight of polyisocyanate to cellulosicmaterial; and wherein the core has a shear strength of from at leastabout 10 to about 30 psi and a shear modulus of from at least about 500psi to about 1,000 psi.
 29. A panel according to claim 28 including athermal reflective material overlaying at least one of the cover sheets.30. A panel according to claim 28 including a respective blowing agentretaining sheet between the core sheet and each of the cover sheets. 31.A panel according to claim 28 in which the cover sheets comprisecellulosic liner material impregnated with from about 8 percent to 15percent by weight of polyisocyanate to cellulosic material, having amachine direction linear expansion at from 50 percent to 90 percenthumidity and 65° F. of less than 0.1 inch per inch in the majordirection, and having a water vapor transmission rate of at least 3.5perms.
 32. A panel according to claim 28 including a respective blowingagent retaining sheet between the core sheet and each of the coversheets.
 33. A panel according to claim 28 including a thermal reflectivematerial overlaying at least one of the cover sheets.